Aerobic Baeyer–Villiger oxidation of ketones to corresponding esters was performed using metal-free carbon as a solid catalyst and benzaldehyde as the sacrificing agent. Several carbon materials were tested for the oxidation of cyclohexanone to ε-caprolactone, and it was found that Ketjen Black showed the highest catalytic activity, over 90% of ε-caprolactone yield at 50 °C. A catalyst recycling test suggests that the catalyst has high durability under the reaction condition of oxygen atmosphere at 50 °C. Mechanistic study suggests that peracid species produced by a series of chain propagation reactions is the key intermediate, and the carbon catalyst contributes to high aldehyde efficiency by buffering the radical species, which are essential for the chain propagation reactions.

The incorporation of nitroxide radicals into a nitric acid-assisted carbon-catalyzed oxidation system (NACOS) afforded a highly efficient, widely applicable, non-metallic approach for the selective aerobic oxidations of alcohols. Without any solvent, this novel protocol has the ability to oxidize various primary alcohols to their corresponding aldehydes with selectvities as high as 99% at full conversions, with only 0.1 mol% of nitroxide radicals and < 4.5 wt% of activated carbon under mild conditions (temperatures as low as 50 8C and atmospheric pressure).The performances of several stable nitroxide radicals have been compared. The effects of nitric acid concentration, activated carbon loading, and temperature have been studied for the oxidation of benzyl alcohol. The enhanced NACOS represents a greener and more efficient fundamental chemical process, due to its use of molecular oxygen as an oxidant, and its solvent-free nature.